Magnesium alloy



In Drawing.

Patented Oct. 4, 1932 UNITED STATES PATENT, OFFICE,

JOHN P. WETHEBILL, 3D, OF WASHINGTON, DISTRICT OI! COLUMBIA, ASSIGNOR TO AMEBIGANMAGNESIUM,METALS CORPORATION, OF PITTSBURGH, PENNSYLVANIA,

A conrona'rron or nnmwann Y maennsrom ALLOY This invention relates to improvements in alloys andmore particularly to an improved magnesium base alloy.

As is known, there is a considerable demand in technical fields for alloys which combine the desirable properties of light weight and relatively high mechanical strength. Heretofore a number of magnesium alloys have been proposed to fulfill these requirements.

I have found that a very satisfactory alloy combining the desirable properties of lightness in weight, together with relatively high tensile strength and satisfactory resist ance to corrosion, may be prepared by alloying minor amounts of cobalt with magnesium. The alloy may very simply be made up by adding small quantities of cobalt to molten magnesium maintained under a flux. The preferred form of flux maycomprise a mixture of magnesium chloride, potassium chloride and sodium fluorider "Preferably the vessel in which the alloying is carried out is lined: with magnesium oxide or some equivalent materialso as to maintain the components of the final alloy. in a relatively pure condition, and particularly to maintain it free from iron and especially from metals which are decidedlyelectro-negative to magnesium, such for example as copper.

The process hasbeen actually carried out for the manufacture of an alloy in which a quantity of magnesium was fused in a vessel, and out of contact with iron, and to which cobalt in smallamounts was added. In carrying out the process it isadvisable to either add the cobalt in small amounts to the mass of molten magnesium or to provide some method of cooling in the event that the cobalt is added in relatively large quantities, since the reaction is quite exothermic and if too much heat is generated, burning of the magnesium occurs.

As a typical example of, the method of manufacture and of the alloy a small quantity of cobalt was added to a quantity of magnesium which was substantially free from copper and iron. It was found thatthe comcarried out in a vessel lined with I Application filed May 8, 1931. Serial No. 588,075.

magnesium oxide and the molten ma esium was protected from the air with a con stituted by a mixture of magnesium chloride, potassium chloride and sodium fluoride. The alloy was allowed to cool and a small sample was analyzed to determine particularly theforeign elements and the percentage of cobalt. 1 The percentage of cobalt was determined by dissolving a piece in hydrochloric acid solution and then treating with I nitro-beta-naphthol to precipitate the cobalt. It was found that the alloy'contained approximately .5% of cobalt and was substantially free from copper and iron.

The hardness of the alloy of the above composition was determined by a Rockwell machine using a ball and a 100- kilogram load. Several tests of the hardness disclosed values varying from 82.8 to 87.4, and more specifically four readings disclosed the following hardness numbers: 82.8, 85.4, 87.5 and 87.4. The hardness of this alloy, it will be noted, compares very favorably with known commercial alloys. For example pure magnesium (99.9) extruded at 300 C., has a hardness of 46 (100 R, B i. e. the hardness number ,of 46 using the Rockwell machine with a 100 kilogram-javeight and a 050 C. The above mentioned standard alloy, on being rolled and heat treated at 450 C. and quenched, had its hardness increased to 59.6 (100 R, B and disclosed an in ball)- This sample of magnesium has a crease intensile strength. This same commercial alloy, namely the ternary magnesium aluminum manganese alloy, when extruded at 290 C. and rolled at 450 0., has its hardness increased to 7 0.1 (100R, B

It was found that additional amounts of cobalt, when alloyed with magnesium, likewise produced improved alloys. Thus, for example, cobalt may be added to magnesium to produce binary alloys having a fraction of a percent of cobalt up to approximately 5%. In making up alloys with these higher percentages of cobalt'care should be exer-, cised in effectively cooling the mass, because as the cobalt percentage increases the exothermic heats of reaction increase to very near the burning point of magnesium.

It will be seen from a comparison of an alloy of. the present invention with those of known commercial magnesium alloys that it is characterized by an exceptionally high degree of hardness and even-in the unworked condition has a higher degree of hardness than other commercial alloys.

It will also'be observed that inasmuch as the alloy-as made up is substantially free from copper and contains as a secondary component an element which is relatively close to magnesium in the electrochemical series,

the tendency of the alloy to corrode due to galvanic action is relatively slight.

It is further found that the magnesium cobalt alloy is readily workable and machines very well. It is additionally characterized with a relatively high tensile strength. It will be understood, as recognized by those skilled in the art, that the mechanical properties of the alloy may be improved within determinative or'permissive limits by increasing the proportion of cobalt, and that similarly the mechanical properties may be improved by worln'ng and heat treatment.

While a preferred embodiment of the in- Q vention has been described, it is to be understood that this is given merely by way of example of the underlying principles of the invention. It is recognized that magnesium has been widely used as a deoxidizer in metallurgical operations and that proposals have been made to increase its efliciency as a deoxidizer bygalloying it with very large proportions of heavy metals for the purpose of improving 'ts characteristics for this purpose.

These deoxidizers are in no proper sense com mercial alloys. The present 1nvent1on,therefore, is to be sharply distinguished from such prior disclosures and relates to commercial alloys containing a relatively minor percentage of cobalt so as to produce an article which is characterized by a very low specific gravity as well as satisfactory mechanical proper- I claim:

1. A light weight alloy comprising from to 99% of magnesium and the remainder cobalt.

2. A light weight binary alloy comprising approximately 99% of magnesium and one percent of cobalt. In testimon whereof I afiix my signature.

J HN P. WETHERILL, 30. 

